Azo dyes have wide spectrum range and are synthesized with many categories, are widely used in textile printing and dyeing, printing, paper, cosmetic and other industries. It is a very important category of dyes. The preparation of azo dye mainly consists of diazotization reaction and coupling reaction technology, but the coupling reaction is an exothermic reaction, diazo salt is unstable to heat, so coupling reaction of intermittent technology applied in industry all should be carried out with cooling, usually with ice water bath to cool and the temperature is maintained at 0˜5° C. However, in the existing intermittent coupling reactions, diazo salt stay too long in the reactor, the batch reactor is overheated, diazo salts may be decomposed easily, which leading to low yields, low quality and great energy consumption, all batches of products differ in shade, intensity, and so on. Using continuous process production technology, controlling diazo salt and coupling component to rapidly and equally contact, the heat released from reaction quickly transfers away from the reaction media, which can greatly improve product quality and yield of azo dyes, reaching quality stability requirements about dye products by dying industry from root. Furthermore, water-soluble azo dyes preparation reaction is carried out at room temperature in the device without external cold source, which has obvious energy saving features to achieve energy-saving, high efficiency and high quality production of water-soluble azo dyes.
Due to the short reaction time, high productivity, continuous synthesis technology plays a very important role in chemical synthesis, in particular micro-reactor with excellent thermal performance. Robert C. R. Wootton et al. use aniline diazo salts and 2-naphthol to carry out coupling reaction to synthesize azo dyes in micro-reactor. Crane Company (Org Pro Res and Dev, 2004, 8:440, 454; CN01121867.3; CN01804731.9) performed the synthesis of pigment products using micro-reactor technology, the process consists of three steps: diazotization reaction, coupling reaction, pigmentation reaction. In the first step, two liquids carry out diazotization reaction in a micro-reactor, followed by coupling reaction of diazo salt solution and coupling component in second micro-reactor, and finally carrying out pigmentation reaction in third micro-reactor. The results of reaction show that pigment particles has an average diameter of 90 nm with micro-reactor, while the resulting particle size with a conventional reactor is 598 nm, and pigment particle size distribution from micro-reactor has been dramatically narrowed. Using micro-reactors, the color strength (Color Strength) of product than that resulted from conventional reactors has been increases by 19%˜39%; the brightness (Brightness) increases 5˜6 levels, transparency (Transparency) has been increased by 5˜6 levels. However, the production process of micro-reactor is quite complex and the equipment are expensive, and once the passages are plugged, it is difficult to clean. It only applies to reaction that will not lead to jam and small amount of micro-reactor materials handling. It is difficult to apply in large-scale dye production.